Mamba Monster dead?

[Pdelcast]

Originally Posted by GriffinRU

Nice caps, what ESR value they present and why your inductor is not as compact as caps? Ceramics should have zero, but this high capacity once must have some, more care about power ratings for them and cooling.

What do you mean by "Fets are snubbed" i.e. on-die or with the caps network?

By the way which component is failing, or it is too much to ask?

The ceramics show about .005 ohm or so. The inductor isn't as compact as the capacitors because there isn't any inductors as compact as the capacitors -- not really sure what you mean. The smallest 22uh 4 amp inductors are at least 10mm square.

The FETs are snubbed using an RC snubber -- to prevent ringing.

The component that is failing is the switcher controller -- a National LM3485. National is looking into it with us -- seems the overcurrent circuit is failing internal to the LM3485, and leaving the chip in constant overcurrent state. That's why the output voltage drops to 1.08V - -it's in hiccup overcurrent mode. Replace the LM3485, and all works well again.

Patrick

Originally Posted by Pdelcast

The ceramics show about .005 ohm or so. The inductor isn't as compact as the capacitors because there isn't any inductors as compact as the capacitors -- not really sure what you mean. The smallest 22uh 4 amp inductors are at least 10mm square.

The FETs are snubbed using an RC snubber -- to prevent ringing.

The component that is failing is the switcher controller -- a National LM3485. National is looking into it with us -- seems the overcurrent circuit is failing internal to the LM3485, and leaving the chip in constant overcurrent state. That's why the output voltage drops to 1.08V - -it's in hiccup overcurrent mode. Replace the LM3485, and all works well again.

Patrick

for the techies
http://www.national.com/pf/LM/LM3485.html

[GriffinRU]

Originally Posted by Pdelcast

The ceramics show about .005 ohm or so. The inductor isn't as compact as the capacitors because there isn't any inductors as compact as the capacitors -- not really sure what you mean. The smallest 22uh 4 amp inductors are at least 10mm square.

The FETs are snubbed using an RC snubber -- to prevent ringing.

The component that is failing is the switcher controller -- a National LM3485. National is looking into it with us -- seems the overcurrent circuit is failing internal to the LM3485, and leaving the chip in constant overcurrent state. That's why the output voltage drops to 1.08V - -it's in hiccup overcurrent mode. Replace the LM3485, and all works well again.

Patrick

Is it possible that having 2 Fet's tripping the overcurrent, meaning your sense resistor (via Fet) readings are not consistent and Isense is way to sensitive from IC to IC? I am assuming that it is 1 fet per IC (6pin, close to inductor).

Yes, 4 amps inductor is hard to find, but I thought that you can get openframe ones and direct solder them to pcb.

[phatmonk]

Originally Posted by Pdelcast

The ceramics show about .005 ohm or so. The inductor isn't as compact as the capacitors because there isn't any inductors as compact as the capacitors -- not really sure what you mean. The smallest 22uh 4 amp inductors are at least 10mm square.

The FETs are snubbed using an RC snubber -- to prevent ringing.

The component that is failing is the switcher controller -- a National LM3485. National is looking into it with us -- seems the overcurrent circuit is failing internal to the LM3485, and leaving the chip in constant overcurrent state. That's why the output voltage drops to 1.08V - -it's in hiccup overcurrent mode. Replace the LM3485, and all works well again.

Patrick

Thanks for your personal involvement in this issue Patrick.Both of my Monsters have died you guys received one of them last wednesday and no one has called me so I am assuming you ars fixing it.It will be interesting to see how long it will be till I get the first one back.I will be sending the other one in when I get the first defective Monster back.I now have no speedcontrols so pleeeeeeeeeeeeeeeeease fix it soon.

thanks
Will